Field of the Invention
The present invention relates to a technique for suppressing influence of flicker occurring under an artificial light source such as a fluorescent light in particular.
Description of the Related Art
In recent years, an imaging apparatus, such as a digital camera and a cellular phone camera, has been improved in sensitivity. Therefore, a bright image with reduced image blur can be obtained by a high shutter speed (i.e., a short exposure time) imaging even under a comparatively dark environment, e.g., indoors.
The fluorescent lamp generally used as an indoor light source causes flicker, i.e., a phenomenon in which an illumination light periodically flickers, by influence of a frequency of the commercial power supply. A high shutter speed imaging performed under such a light source causing the flicker (hereinbelow, referred to as a flickering light source) may cause unevenness in exposure and color in an image or cause variation in exposure and color temperature among a plurality of continuously captured images.
To solve this problem, Japanese Patent Application Laid-Open No. 2006-222935 discusses a technique in which the state of flicker of an illumination light is detected and, if an exposure time is shorter than a blinking period of the flicker, an imaging timing is adjusted so that the center of the exposure time can be approximately matched with timing at which the amount of the illumination light indicates a maximum value.
However, the following problem occurs because the technique discussed in Japanese Patent Application Laid-Open No. 2006-222935 adjusts each of the imaging timing at which a plurality of images is continuously captured based on the phase of the maximum value of the amount of the illumination light detected before starting to continuously capture a plurality of images.
In general, it has been known that the frequency of the commercial power supply fluctuates with respect to a reference frequency (for example, fluctuate of ±0.2 Hz in Japan). More specifically, the flicker of the flickering light source causes a fluctuation about twice as much as the fluctuation of the commercial power supply with respect to a reference blinking period. For this reason, a difference in timing tends to be large between a peak timing of light amount of the flickering light source obtained from the detection result of flicker and an actual peak timing of the light amount of the flickering light source according as time elapses after the flicker is detected.
In the technique discussed in Japanese Patent Application Laid-Open No. 2006-222935, therefore, as an image is captured later in continuously capturing a plurality of images, the difference between the peak timing obtained from the detection result and the actual peak timing become greater. Consequently, it becomes more difficult to suppress the influence of the flicker.